1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter, referred to as "LCD") device, and more particularly to an LCD device in which a repair line can be substituted for a defective bus line by spot-fusing of a laser when a defect such as open-circuited portion or short-circuited portion between bus lines occurs in a lower substrate on which a plurality of thin film transistors are arranged in matrix.
2. Description of the Prior Art
Generally, in fabrication sequence of LCD device, if a gate bus line or a data bus line is open-circuited or short-circuited in a thin film transistor (hereinafter, referred to as "TFT") array, such an LCD panel is distinguished as a defective panel.
To eliminate a defect caused by the open-circuited portion or short-circuited portion of a bus line, an LCD device is provided with a repair line which is formed in outside part of a plurality of TFTs on a lower glass substrate. Thus, when a defect such as short-circuited portion between gate and data bus lines or open-circuited portion of each bus line occurs, the repair line is substituted for a defective bus line, thereby allowing the TFT to be normally operated.
FIG. 1 is a plane view showing a lower glass substrate in a prior art LCD device.
In FIG. 1, the prior art LCD device has a plurality of gate bus lines 1, a plurality data bus line 3, and a repair line 5. The gate bus lines 1 are spaced from each other and arranged in row direction. Each of the gate bus lines 1 is connected to a corresponding gate pad la for receiving an externally applied signal and commonly connected to each gate electrode of a plurality of TFTs (not shown).
The data bus lines 3 are spaced from each other and arranged in column direction to be intersected with the gate bus lines 1. Each of the data bus lines 3 is connected to a corresponding data pad 3a for receiving an externally applied signal and commonly connected to each source electrode or each drain electrode of the TFTs.
Also, the repair line 5 is formed in outside portion of the lower glass substrate 10 except a portion in which the TFTs connected to the gate and data bus lines are formed, and is connected to a repair pad 5a for receiving an externally applied signal. The repair line 5 is intersected with the data bus lines 3 in row direction and is intersected with the gate bus lines 1 in column direction.
After fabrication of a lower panel having the above-mentioned array structure on the lower glass substrate, a defect checking process is performed. In this defect checking process, it is possible to check whether the lower panel is normally operated or not, i. e. is defective or not.
In the defect checking process, if a short in circuit occurs in a crossing portion 2 of the gate and data bus lines 1, 3 in the lower panel, a cutting process is performed to cut both ends of one of the short-circuited bus lines and then a repair process is performed to connect the gate bus line 1 or the data bus line 3 corresponding to the short-circuited crossing portion with the repair line 5 by spot-fusing of a laser. As a result, the defective panel can be normally driven.
On the other hand, in case that an open in circuit occurs in a crossing portion 2 of the gate and data bus lines, a repair process is performed to spot-fuse a crossing portion 7 between the gate bus line 1 or the data bus line 3 and the repair line 5 with an insulating layer interposed therebetween and connect the gate bus line or the data bus line with the repair line.
Repairing operation at a crossing portion 7 between the repair line 5 or a gate bus line 1 or a data bus line 3 is described in detail with reference to FIG. 2.
FIG. 2 is an enlarged view of a crossing portion 7 between a repair line and a gate bus line 1 or a data bus line 3 in a lower panel of the prior art LCD device.
As shown in FIG. 2, since in the prior art LCD device all the gate and data bus lines 1, 3 are intersected with the repair line 5, the prior art LCD device has the crossing portion 7 of the gate and data bus lines. In the crossing portion 7, the gate and data bus lines 1, 3 are electrically insulated with each other with an insulating layer (not shown) interposed therebetween.
Therefore, after fabrication of an LCD panel, an electric power is applied to bus lines and then it is checked whether an open or a short of bus lines is generated or not. If an open of a bus line, i.e. a defective bus line is detected in the checking process, the crossing portion 7 between the defective bus line and the repair line 5 is spot-fused by a laser, whereby the repair line 5 can be electrically connected with the defective bus line. When short-circuited bus lines at the crossing portion 2 are detected, after cutting both sides of one of the short-circuited bus lines, 3, the crossing portion 7 between the bus line cut thus and the repair line 5 is spot-fused by a laser to connect the repair line 5 with the bus line cut thus. With repairing of a defective bus line, TFTs of the lower panel can be normally operated.
However, since in the prior art LCD device a repairing portion is a crossing portion between the repair line 5 and a defective bus line (a gate bus line or a data bus line), there arises the problem the repair line 5 is frequently cut when the repair line is spot-fused by a laser. That is, a repairing error is frequently generated. Also, there arises another problem that a repaired portion too, has to be cut, when a repair line is cut. In case of occurrence of such a repairing error, the re-repairing process can not be performed in the construction of the prior art LCD device